Presentation on theme: "Sally Seidel 1 3D Sensor Studies at New Mexico Sally Seidel for Martin Hoeferkamp, Igor Gorelov, Elena Vataga, and Jessica Metcalfe University of New Mexico."— Presentation transcript:
Sally Seidel 1 3D Sensor Studies at New Mexico Sally Seidel for Martin Hoeferkamp, Igor Gorelov, Elena Vataga, and Jessica Metcalfe University of New Mexico
Sally Seidel 2 Introduction We have characterized 3D sensors of pitch 200 µm × 100 µm. We report probe station based studies of depletion voltage, leakage current, electrode capacitance, capture time, and signal rise time, supported by simulations The devices: non-irradiated and irradiated (10 14, 2×10 14, 10 15 cm -2 55-MeV-p), unannealed, from Sherwood Parker.
Sally Seidel 4 3D Sensor Configuration Top view layout Layout dimensions: 200 m x 100 m spacing, 17 m electrode diameter, 121 m electrode length. Configuration of the devices: p-type silicon. –Alternating columns of n- and p-electrodes –Most electrodes are connected together along each column –Some electrodes are left isolated, to be contacted and measured individually
Sally Seidel 5 Electrode Leakage Current Measured leakage current versus fluence: Prior to irradiation, the n-electrodes are shorted together by a surface electron layer.
Sally Seidel 6 Electrode Depletion Voltage Pixel cell depletion voltage measured via pulse height: Pixel cell depletion voltage measured via LCR meter:
Sally Seidel 7 Array Depletion Voltage To test the entire device, we completely flood the 3D sensor with a uniform 1064 nm laser spot and scan the bias voltage above full depletion. Photo with IR filter of laser illuminating the sensor:
Sally Seidel 8 Array Depletion Voltage Array depletion measured from signal efficiency (pulse height relative to the maximum for the non-irradiated device) versus bias: Result: very low values of depletion voltage for the entire sensor array, V depletion ~ 15V for non-irradiated sensor V depletion ~ 60V for sensor irradiated to 2x10 14 V depletion ~ 130V for sensor irradiated to 1x10 15
Sally Seidel 10 Electrode Capacitance Electrode capacitance versus temperature and frequency:
Sally Seidel 11 Electrode Capacitance Direct measurement is checked by indirect measurement through signal decay time : PICOPROBE 35 R= 1.25M C=.05pF To Oscilloscope Pulsed1064 nm and 960 nm Laser +Vbias Gnd Indirect measurement using decay time of IR pulse on an isolated electrode. Electrode is grounded through input impedance of a Picoprobe 35. The IR laser induced charge is collected. When the laser is turned off the signal decay follows an exponential with a time constant = R*(C+C 3D ), referred to here as RC time constant. C 3D is extracted from the decay time constant using values of probe resistance and capacitance.
Sally Seidel 12 Electrode Capacitance Performed at different bias voltages, using the procedure of Parker et al., Proc. IEEE Trans. Nucl. Sci., Oct 2001, p. 1635: Isolated electrode grounded through the 1.25 MΩ input impedance of the picoprobe. T = 0 when the laser is turned off. After the light emission ends and the charge is collected, the pulse height follows an exponential of time constant 177 ns. Averaging the values for 50 V to 100 V gives a p-electrode capacitance of 91.6 fF. Irradiated 2×10 14 cm -2 55-MeV-p sensor p-electrode
Sally Seidel 13 Electrode Capacitance A summary of the capacitance versus fluence for a p- and an n-electrode using the direct capacitance measurement technique and for the p-electrode using the indirect measurement technique. The indirect measurement gives about a 50fF higher result.
Sally Seidel 14 Electrode Capacitance Calculation 3D electrostatic calculation (IES Coulomb): –p electrode length = 121 µm –p electrode diameter = 17 µm nominal –Center electrode to nearest neighbors Prediction for p electrode = 28 fF nn nn ppp Capacitance at 17 m is 28 fF We are systematically varying the geometrical parameters to understand the impact of each one on capacitance. An example for electrode diameter:
Sally Seidel 15 Position Scans Scan the laser across one electrode cell to measure uniformity of signal collection Y X
Sally Seidel 16 Position Scans Signal collection versus position: Non-irradiated 3D sensor, p-electrode X Y
Sally Seidel 17 Charge Collection Pulse the IR Laser as fast as possible and observe the rise time of the signal PICOPROBE 35 R= 1.25M C=.05pF Pulsed1064 nm IR Laser +Vbias Gnd Measure the output rise time while reducing the laser pulse duration
Sally Seidel 18 Charge Collection Input 0.3 nS laser duration: Output irradiated (10 15 ) p electrode, ~1.5 nS rise time Output non-irradiated p electrode, ~ 2.5 nS rise time NOTE: The system isolation was improved, and a broken cable shield replaced, after this measurement was recorded. Revised graphs are in preparation.
Sally Seidel 19 Capture Time For an irradiated 3D sensor, pulse the laser at a distance of 30 µm from the electrode and measure the output. Repeat with laser pulse at a distance of 90 µm.
Sally Seidel 20 Capture Time The 60 µm difference in laser position results in a collection time difference of 50.6 nS – 47.4 nS = 3.2 nS NOTE: The system isolation was improved, and a broken cable shield replaced, after this measurement was recorded. Revised graphs are in preparation.
Sally Seidel 21 Plans Plans for 2007-2008: –Repeat charge collection and capture time measurement with new low-noise system. –Complete systematic simulation of full scope of geometrical options. –Implement TCAD device simulation for improved capacitance and charge collection prediction. –Systematics studies with 820 nm and 960 nm lasers. –Irradiate ATLAS geometry devices at LANL and Sandia. –Apply these measurement techniques to the ATLAS geometry devices. There is a larger range of measurements we would like to do additionally if a TurboDAQ system becomes available. We are 5 people available for testbeam staffing as well.
Sally Seidel 22 Budget for FY 2008 $110,000 for electrical engineer, travel, and materials and supplies.